The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, the oil pump of a vehicle engine is usually a rotor pump. The rotor pump comprises a shell, and inner and outer rotors eccentrically disposed in the shell. The shell comprises an inlet connected to a low-pressure oil chamber, and an outlet connected to a high-pressure oil chamber. When the engine is in operation, the inner rotor is driven to rotate with the outer rotor. With the rotation of the inner rotor and the outer rotor, the low-pressure oil injected through the inlet is transformed to high-pressure oil and then discharged from the outlet. However, in conventional oil pumps, the high-pressure oil chamber and the low-pressure oil chamber are usually disposed on the opposite sides, so that the structure of the oil pump is not compact and occupies a big space, which is disadvantageous for miniaturization of the oil pump as well as the engine having the oil pump.